BIOL 112 Lecture Notes - Lecture 4: Keratin, Nitrogenous Base, Hemoglobin

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BIOL 112 Full Course Notes

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Biol 112 lecture 4 teriary & quaternary structure. Interacions that determine the teriary structure of proteins: side chain interacions: H-bond (side chain + carbonyl group on backbone) Hydrophobic interacions + van der waals interacions. Ionic bond: disulide bond is the only kind of covalent bon in a protein, apart from the pepide bond (which links aa"s), and 2 cysteines, aa = cysteine, only aa that has a sh group. Quaternary structure dimer: 2 idenical proteins that come together to form a larger structure = quaternary structure (tetramers, (ex. hemoglobin) etc, = larger) quaternary structure is a bunch of fully folded proteins (subunits) together (not necessarily idenical) Primary: the sequence of aa in a polypepide pepide bonds. Secondary: formaion of alpha helices and beta pleated sheets in a polypepide: h-bonding between groups along the pepide-bonded backbone, depends on the primary structure.

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1. The level of protein structure that is stabilized primarilyby non-covalent interactions between the side chains within asingle polypeptide chain is refered to as its:

A) primary structure

B) secondary structure

C) tertiary structure

D) quaternary structure

E) none of the above

2. Collagen, a strong fibrous protein found in connectivetissue, bone, and the extracellular matrix, has a structure inwhich three left-handed helices wind around each other to form aright-handed triple helix. The primary structure of collagen has arepeat unit of -(Gly-X-Pro)- Which of the following bonds stabilizethe collagen triple helix? (mark all that apply)

A) Hydrogen bonds between hydroxyproline residues

B) Hydrogen bonds between N-H and C=O

C) Ionic bonds between amino acid side chains

D) Hydrogen bonds between charged amino acids

3. The non-covalent forces that stabilize the Beta-strandconformation of peptides include:

A) H-bonds between amide C=O and amide NH

B) Van der Waals packing between the peptide backbone atoms

C) Van der Waals packing due to side chain interdigitation

D) Only A and B above

E) None of the above

4. What is the approximate length difference of a 22-kDasingle-stranded ?-helical protein segment vs. a 22-kDasingle-stranded ?-strand protein segment? Assume a mean residuemass of 110 Da. Show work.

5. Circular dichroism measurements have shown that the peptidebackbone of poly-l-lysine (KKKKKKK) adopts a random coilconformation at pH 7.0, but becomes ?-helical as the pH is raisedabove 10. This observation is known as the

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BIOL 112 Lecture Notes - Lecture 4: Keratin, Nitrogenous Base, Hemoglobin

BIOL 112 Full Course Notes

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